The subject invention relates to the polyester compositions reducing molding warpage and being superior in mechanical properties, surface appearance and plating characteristic; to the moldings of the compositions; and to the processes for manufacturing the moldings.
Considerably increasing in strength and flexural modulus when a reinforcement or a filler is added, the thermoplastic polyester resins represented by polybutylene terephthalate are used extensively for parts of electrical and electronic equipment, automobiles and so forth. The reinforcements and fillers such as glass fibers and micas producing reinforcing effects are known to generally have a fault of giving large warpage to their moldings because of the shapes being fibrous or laminar.
Further, the moldings of the thermoplastic polyester resinous compositions to which a reinforcement or filler is added lose smoothness of surface because they are affected thereby, they cannot be, therefore, used at all when the surface appearance and smoothness of moldings are significant.
It is proposed for reducing molding warpage to add small-anisotropy granular fillers such as calcium carbonates, clays, diatomaceous earthes, calcium metasilicates, talcs and sericites (Japanese Laid-Open Patent No. 75245/1978). This method, however, has a defect in that the thermoplastic polyester resinous compositions are neither satisfactorily practicable because of the decrease in mechanical properties such as impact strength nor improved in surface smoothness at all, although molding warpage is reduced.
The known methods for metallizing the surface of the thermoplastic polyester resins through plating include that wherein those containing a filler similar to those aforementioned are subjected to etching by using an alkaline solution and then plated (Japanese Laid-Open Patent No. 15977/1979), that wherein those being reinforced with a glass fiber and calcium carbonate are subjected to etching by using an alkaline hydroxide solution containing an oxidizing agent and then plated (Japanese Laid-Open Patent No. 6374/1978) and that those reinforced with a glass fiber are immersed in an aqueous solution of nitric acid and in an alkaline hydroxide aqueous solution in turn for etching and then plated (Japanese Laid-Open Patent No. 6376/1978). They can, however, obtain no highly practicable metal-plated thermoplastic polyester resin moldings because the adhesion and surface gloss of metal-plated layer reach no substantially effective level.